1. Field of the Invention
This invention relates to a laminated organic photosensitive material which has a charge producing layer and a charge transporting layer formed on an electroconductive support and which is not only readily electrified, but also has a small residual potential. More particularly, the invention relates to a laminated organic photosensitive material which has a high sensitivity to a semiconductor laser region wavelength so as to be suitable for use as a photosensitive material for a laser beam printer.
2. Description of the Prior Art
A composite or laminated type organic photosensitive material has been developed and put to practical use in recent years. This type of organic photosensitive material is disclosed in, for example, Japanese Patent Publications Nos. 42380/1980 and 34099/1985. It comprises an electroconductive support, a charge producing layer formed on the support and a charge transporting layer formed on the charge producing layer. For instance, such a composite photosensitive material has an electroconductive support of aluminum layer, a charge producing layer formed on the aluminum layer, and a charge transporting layer formed on the charge producing layer.
The charge transporting layer is formed by, for example, preparing a dispersion of a charge transporting substance together with an organic solvent, a binder resin and, if necessary a plasticizer, applying the dispersion onto the support, and drying to a thin film. The charge producing layer is formed by, for example, dissolving a charge producing substance in an organic solvent together with a biner resin and, if required, a plasticizer, applying the solution onto the charge transporting layer, and drying to a thin film.
There are already known a variety of charge producing substances including phthalocyanine compounds, as disclosed in Japanese Patent Laid-Open No. 166959/1984. A number of charge transporting substances including hydrazone compounds are also already known, as disclosed in Japanese Patent Publications Nos. 42830/1980 and 34099/1985.
The hydrazone compound includes p-N,N-dialkylaminobenzaldehyde-N',N'-diphenylhydrazones, and in particular, p-N,N-diethylaminobenzaldehyde-N',N' diphenylhydrazone is preferred. p-N,N-diphenylaminobenzaldehyde-N'-methyl-N'-phenylhydrazone and p-N-ethyl-N-phenylaminobenzaldehyde-N'-methyl-N'-phenylhydrazone are also preferred.
In general, in the laminated organic photosensitive material, the charge transporting substance has a decisive bearing on the performance or quality of the photosensitive material. The manufacture of a photosensitive material of high sensitivity requires the provision of the charge transporting layer with the charge transporting substance in a relatively high concentration, and therefore the use of a charge transporting substance which is highly compatible with the binder resin. The substance must also be one from which a thin film can be formed easily. Moreover, the charge transporting substance is required to have an appropriately low oxidation potential and a high charge transfer rate so that the charge produced in the charge producing layer may be effectively injected into the charge transporting layer. However, an organic compound which has a low oxidation potential is generally sensitive to oxidation and hence is unstable.
None of the known hydrazone compounds as hereinabove mentioned is always satisfactory in view of the required properties as above set forth. The use of any such hydrazone derivative as a charge transporting substance still fails to provide any laminated organic photosensitive material of high sensitivity. None of any such known hydrazone derivative is satisfactory in stability, either.
Meanwhile, there has been a demand for a laminated organic photosensitive material for use in a laser beam printer which is sensitive to the long wavelength region from about 750 nm to about 850 nm, and the use of a variety of charge producing substances and charge transporting substances have hitherto been proposed. For instance, a number of phthalocyanine compounds including titanylphthalocyanine are disclosed for use as a charge producing substance as being sensitive to the long wavelength region as hereinabove mentioned in the Japanese Patent Laid-Open No. 166959/1984. However, none of them have been found to be charged and sensitive satisfactorily.
It is already known that X-type nonmetal phthalocyanine has a sensitivity to the long wavelength region, and a single layer photosensitive material is disclosed in U.S. Pat. No. 3,816,118. However, the photosensitive material has a very low sensitivity.